4D Multi-Physics Forward Modelling for CO2 Storage Monitoring in the Hewett Field

Long-term geological CO₂ sequestration relies on quantitative time-lapse geophysical monitoring to assess storage integrity. In this study, we present a multi-physics forward modelling framework for 4D monitoring of CO₂ storage and demonstrate its application through a case study in the Hewett Field, a depleted gas field in the Southern North Sea. The case study focuses on a 30-year CO₂ injection scenario into the Bunter sandstone. Seismic, controlled-source electromagnetic (CSEM) and gravity methods are combined within this multi-physics framework to provide complementary information.

The modelling workflow includes geological modelling, CO₂ injection modelling, rock-physics modelling, and 4D geophysical forward simulations. The modelling starts from a static geological model describing the structural framework of the reservoir. This model is used in the dynamic CO₂ injection simulations, which predict the CO₂ saturation and pressure evolution during CO₂ injection and post-injection migration. The resulting dynamic properties are converted into velocity, resistivity and density changes through rock-physics modelling. Based on these physical properties, 4D geophysical forward modelling is performed for seismic, CSEM and gravity methods to simulate time-lapse geophysical responses associated with CO₂ plume development.

By comparing the simulated time-lapse responses of seismic, CSEM and gravity data, the integrated 4D modelling framework uses the Hewett Field as a case study to develop and test a site-specific monitoring strategy.